This invention relates to improved hard body armor which protects the wearer from bullets, shrapnel, etc.
Modern-day body armor dates back to World War II when bomber crews used flak jackets, which were padded jackets containing steel, aluminum, or glass fiber plates combined with heavy nylon textiles.
The main discovery in improving body armor has been the use of heavy-weave nylon-type cloth made of aramid fibers. KEVLAR, sold by DuPont, is one brand of the ballistic cloth. So called soft ballistic armor, is made of multiple layers of woven fabric. The fabrics may be penetrated when yarn in the projectile's path is pushed aside or broken. The over-under weave of fabrics produces spots which are inherently weak where the fibers intersect. Improper interlacing or sewing of the layers of fiber can cause the strain wave to reflect, so that fibers break without dispersing a projectile's energy. Finally, the fibers in woven or sewn armor must overcome a state of crimp before they can be placed in tension.
Soft body armor has also been fabricated from polyethylene cloth. SPECTRA SHIELD, sold by Allied Signal Technologies, is a brand of such ballistic cloth. This material utilizes a unidirectional fiber in layers. The layers are cut, cross-plied (in a 0.degree., 90.degree. orientation) and pressed to produce a single ply; the plies can be stacked to form a pliable material.
When the fibers of soft, woven armor stretch and break, a small fraction of the projectile's energy is absorbed in the process; the rest is transmitted through the armor layer to the body, having the effect of a heavy blow. The more filaments a projectile engages, the more efficient the energy absorption in, and the higher the degree of bullet deformation.
The energy which is not absorbed by the fibers causes backface deformation, in which material is displaced by the projectile's impact and comes into direct contact with the wearer's body. Excessive backface deformation results in severe blunt trauma, which can cause severe injury or death, even when the projectile does not penetrate the armor.
The most important factors to be considered in developing a new kind of body armor are: (1) its ability to prevent penetration of a projectile; and (2) its ability to reduce the amount of backface deformation. Other factors to be considered are the cost of the materials, the techniques of construction, and the comfort of the wearer.
The layering of different ballistic materials has been used to make armor panels of composites, which have greater stopping power than metal plates used in the past.
Protective body armor is classified by the National Institute of Justice (NIJ) based on the level of protection it offers; Class I, Class II, and Class IIIA armor are soft body armor. Class III armor protects from high-velocity rifle rounds 7.62 mm, 150/M-80 ball round and all lesser threats. Class IV protects against the armor-piercing round 30.06, 165/A.P., at 2850 ft/sec., and all lesser threats.